Reliable operation of flight control surfaces, such as wing flaps or slats, in civil and military aviation, is naturally important for ensuring safe and dependable air travel. It is therefore desirable to be able to detect any impairment of function in such movable flight control surfaces before the aircraft is in flight. For safety reasons, these types of flight control surfaces (e.g. high-lift flaps) are typically required to have multiple load path supports, thus providing redundancy. Furthermore, a problem or fault in any one of the load paths should be detectable generally within one flight.
Because of the redundancy provided in the load path supports, each control surface will usually have more than one actuator or drive unit, with each drive unit being powerful enough or having sufficient strength to operate and/or to structurally support the control surface alone. Where one of these load paths is compromised due to a problem or fault, however, it is highly desirable to be able to detect this promptly.